Will expand to 11" for your knuckle to fit and will get as small as 6 1/2" when you pull the end ties together. 
 
If the expansion is too big for you, you can place a new knot on each end the ties and cut it shorter.  For me, I didn't like the long ties touching my arms, so I made it smaller. You can add a dot of super glue to make the knot more secure.